The present invention relates to a semiconductor storage device and its manufacturing method, particularly, an electrically erasable programmable nonvolatile semiconductor storage device and its manufacturing method.
Also, the invention relates to a semiconductor storage device, as well as its manufacturing method, in which semiconductor storage elements and semiconductor switching elements are mounted compositely on one identical substrate.
Also, the invention relates to portable electronic equipment and IC cards equipped with such a semiconductor storage device or semiconductor device.
As a semiconductor storage device, there has conventionally been a flash memory that is a memory element that allows electrical writing and erasing (e.g., see “A handbook for flash memory techniques,” edited by Fujio Masuoka, K. K. Science Forum, Aug. 15, 1993, pp. 55-58). A structural cross sectional view of the flash memory element is shown in FIG. 34. As shown in FIG. 34, the flash memory element is composed of a floating gate 1506 made of polysilicon placed on a semiconductor substrate 1501 via a first oxide 1504, and a control gate 1507 made of polysilicon placed on the floating gate 1506 via a second oxide 1505. On the surface of the semiconductor substrate 1501, a pair of source/drain diffusion regions 1502, 1503 are disposed. The end portions of the gate electrodes 1506, 1507 are respectively laid above the end portions of the source/drain diffusion regions 1502, 1503. The control gate 1507 plays the role of a gate electrode of an Field Effect Transistor (FET) in the flash memory. Moreover, between the control gate 1507 and the semiconductor substrate 1501, the first oxide 1504, the floating gate 1506 and the second oxide 1505 are disposed. Therefore, the flash memory is a memory element which is provided with a memory film (floating gate) serving as a charge retention section disposed in a gate insulator portion of the FET so as to implement the function of changing a threshold voltage of the FET depending on a charge amount stored in the memory film.